LIST OF ILLUSTKATIONS. XIX 



FIGURE PAGE 



109. Diagram of a vertical section through a portion of the lateral 



eye of Limulus polyphemus, showing some of the conical lenses, 

 and corresponding retinulae. a, Cuticle ; bb, cuticular lens ; 

 cc, hypoderm ; Bn, retinula ; n, nerves . . . , . . 160 



110. Euphausia pellucida. /.o, Luminous organ .. ,. .. 161 



111. Luminous organ of ^MjjAaMSj'a. /, Fibres ; e, lens .. .. 162 



112. Eye-stalk of Euphausia. lo. Luminous organ ; a, lower eye . . 162 



113. One of the elements of the eye of a fly. kk, Crystalline cone; 



X, position of the image ; 5, rod ; sc, sheath ; sew, outer 

 sheath ; r, retina ; y, seat of vision . . . . . . . . 166 



114. Photichthys argenteus .. .. .. .. .. .. 185 



115. Ceratius bispinosus .. .. .. .. .. .. 186 



116. Edge of a portion of the mantle of Aglaura hemistoma, with a 



pair of sense-organs, v, Velum ; k, sense-organ ; ro, layer of 

 nettle cells ; t, tentacle 188 



117. Sense-organ of leech. 1, Epithelium; 2, pigment; 3, cells; 



4, nerve . . . . . . . . . . . . . . . . 189 



118. Daphnia pulex. a, Antennai; 6, brain; e, eye; h, heart; m, 



muscle of eye ; n, nerve of eye ; o, ovary ; ol, olfactory organ ; 

 s, stomach ; y, three eggs deposited in the space between the 

 back and the shell 211 



